1. Field of Invention
The invention relates to a rotary optical encoder and, in particular, to a rotary optical encoder with the function of outputting phase-changing signals.
2. Related Art
The rotary optical encoder is primarily used to detect the pole position of a rotor. It contains a light emitter, a light receiver, a code wheel and a code plate in between, and a processing circuit. By properly designing the pattern of code tracks on the code wheel and the code plate, one can readily obtain the required signal output.
The design of a normal servomotor usually uses a rotary optical encoder to detect its rotation position, speed, and direction. If the servomotor is brushless, Hall devices are traditionally used to provide the required rotor position signal so that the current on the stator can correctly change the phase. To save the space and lower the cost, the encoder manufacturers integrate the phase-changing function required by the brushless motor into the encoder. This can provide more accurate phase-changing signals.
With reference to FIG. 1, the normal rotary optical encoder with phase-changing signals usually has three extra tracks on the code wheel. Therefore, the code wheel contains dense slits 1 distributed at equal distance and interpolating code tracks 2, 3, 4 divided also at equal distance. The combination of these three code tracks provides the phase-changing signals on the current of the motor coil.
However, since there are three code tracks on the code wheel, three corresponding light sensors are required. The illumination area has to be increased in order to cover all the light sensors. This inevitably increases the space and cost of the encoder. Therefore, it is imperative to find a better encoder with the required phase-changing function but not the above-mentioned problems.